1. Field of the Invention
The present invention relates to a manufacturing method of an organic semiconductor structure, wherein the organic semiconductor structure comprising an organic semiconductor layer formed with organic semiconductor material having liquid crystallinity, an organic semiconductor structure manufactured by the manufacturing method of and an organic semiconductor device.
2. Description of the Related Art
As a typical example of an organic semiconductor device, an organic field-effect transistor (also called organic FET) using an organic semiconductor as an active layer (hereinafter, referred to as an organic semiconductor layer) can be mentioned. In order to realize a thin film-large area device, the organic FET is required to have uniform charge carrier transport property and high carrier mobility over a sufficient large area.
In this organic FET, the organic semiconductor layer is formed, by vacuum deposition process, from molecular crystals represented by pentacene. It is reported that in a method of forming an organic semiconductor layer by vacuum deposition process, an organic semiconductor layer having high charge carrier mobility, which is greater than 1 cm2/V·s, can be obtained by optimizing film-manufacturing conditions. (see Y. -Y. Lin, D. J. Gundlach, S. Nelson, and T. N. Jackson, “Stacked Pentacene Layer Organic Thin-Film Transistors with Improved Characteristics”, IEEE Electron Device Lett, 18,606 (1997)).
However, generally in the organic semiconductor layers formed by the above-mentioned vacuum deposition process, a large number of grain boundaries easily occur in polycrystal state of aggregated fine crystals, and further, defects easily occur so that such grain boundaries and defects inhibit transportation of charge. Accordingly, when an organic semiconductor layer is formed by vacuum deposition process, it is actually very difficult to form an organic semiconductor layer serving as an element of an organic semiconductor device continuously with uniform performance over a sufficiently large area.
On the other hand, a discotic liquid crystal is known as a material showing high charge carrier mobility (see D. Adam, F. Closss, T. Frey, D. Funhoff, D. Haarer, H. Ringsdorf, P. Schunaher, and K. Siemensmyer, Phys. Rev. Lett., 70,457 (1993)). In this discotic liquid crystal, however, transportation of charge is performed based on 1-dimensional charge transport mechanism along column-shaped molecular alignment. Thus, there is a problem that it is difficult to apply industrially because strict control of molecular alignment is required. Up to now, there is no report on a successful example of a thin-film transistor using the discotic liquid crystal as a material of an organic semiconductor layer.
It has been reported that a rod-shaped liquid crystal material such as a phenyl benzothiazole derivative also shows high charge carrier mobility in a liquid crystal state (see D. Adam, F. Closss, T. Frey, D. Funhoff, D. Haarer, H. Ringsdorf, P. Schunaher, and K. Siemensmyer, Phys. Rev. Lett., 70,457 (1993)). However, there is still no report on a successful example of a thin-film transistor using the rod-shaped liquid crystal material in an organic semiconductor layer. The rod-shaped liquid crystal material occurs in several liquid crystal states, and as the structural regularity of the liquid crystal material is increased, the mobility of charge tends to be increased. However, when this liquid crystal material is transferred into a crystal state of higher structural regularity, the mobility of charge is reversely decreased or not observed, thus naturally failing to exhibit the performance of a thin-film transistor.
When a polymer material in a molecular dispersion system is used as an organic semiconductor material, an organic semiconductor layer, which having uniform charge transport property over a large area, can be formed by coating this organic semiconductor material. However, the charge carrier mobility of the resulting organic semiconductor layer is as low as 10−5 to 10−6 cm2/V·s, and is problematic because of its dependency on temperature and electric field.